Mixtures
Until recent times, instruments operating on mechanical and radioisotope principles have been in use for measurements of density of mixtures conveyed in pipelines. To the instruments operating on mechanical principle belongs, for instance, a meter metering the weight of mixture conveyed versus the known volume of this mixture, together with a system indicating the weight of the instrument itself. The operating principle of a meter of this type is based on measurement of the weight of a certain section of pipeline together with the weight of mixture conveyed through the said section of the pipeline. The weight of such a pipeline section depends on the density of the mixture which is being conveyed through the said section. Equipment of another type designed for direct measurement of density of mixtures conveyed in pipelines is a radioisotope instrument in which the effect of gamma ray absorption by the measured medium is used.
This type of instrument includes a gamma radiation source, said source being installed in the pipeline, and a system which receives the beam of radiation, said system translating the intensity of variations in absorption of rays by the mixture into an electric signal. This signal is then transmitted to an indicator-recording system. Operation of instruments of the above described type is based on principles other than measurement of electrical performance of the mixture and then on translating of variations in this performance into an electric or other signal.
One imperfection of instruments of the above described type is the complex construction required for the system translating the signal of the sensing element into an electric signal, while also there is a high time constant associated with inertia of the instruments, and a comparatively low accuracy of density measurements. Besides, in the case of using of a radioisotope-type instrument the operator may be exposed to harmful effects of radiation.